Voltage regulation

I have noticed that my dedicated mains power slowly fluctuates between 124 and 127 volts. Nothing seems to correlate like furnace - refrigerator turning on and off - time - day of the week etc. I'm looking for something that would keep the output a steady 120V without constricting the current. I'm not looking to break the bank but would like any and all suggestions.

The reason I'm looking for this is because I have a tube integrated where the bias goes up and down with the voltage fluctuations.

Thanks